Implement read! for LP file format

[odow]

MathOptInterface.jl/src/FileFormats/LP/LP.jl

Lines 289 to 291 in c34a594

	function Base.read!(io::IO, model::Model)
	return error("read! is not implemented for LP files.")
	end

[odow]

There's an old implementation here that could be tidied up: https://github.com/odow/LPWriter.jl/blob/master/src/reader.jl

[guilhermebodin]

Hi, @odow I am giving it a try. Might open a PR this week.